gdb for Riscv, single stepping issue

James Becker
Mon Jun 27 20:40:02 GMT 2022


I have a RISCV-EL2 core running in a Nexys A7 FPGA board.

I have openocd for riscv running over jtag with a connection by 
riscv-gdb to the openocd instance at port 3333.

Everything works fine, stepping, break points, load, view memory.

But I have one issue: Some of the memory in my design is 4 byte 
aligned.  Its designed for fast instruction fetch, its known as ICCM.

When I have code running in that memory, gdb still works fine for 
breakpoints, but it will not single step.

Looking at the openocd debug files, it appears that gdb is attempting to 
do a 2 byte read as a part of the single stepping procedure.

Since my memory does not support 2 byte reads or writes, this fails.

Is there some way that gdb can be configured to not do any 2-byte word 
reads or writes during single stepping?  I can't seem to find any.

Jim Becker
CrossFire Technologies Inc
1000 Westgate Dr. Suite 150-I
St. Paul, MN 55114
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